Conventional electric motors include a rotor and a stator. One or both of the rotor and the stator usually includes a magnetic core. The main ingredient of the magnetic core is iron which can easily be oxidized in air to produce iron oxide or rust, which affects the appearance of the magnetic core and the performance of the motor. Currently, tinplating is mainly used to prevent iron oxidation. However, tinplating severely pollutes water. In addition, tin is usually plated on the surface of the iron core and, as a result, those surface sections that are not tinplated can be easily oxidized. Moreover, tinplating is an expensive process.